1. Field of the Invention
This invention relates to the preparation of polyamides and is more particularly concerned with the preparation of polyamide block copolymers and certain azetidine-2,4-dione prepolymer intermediates therefor.
2. Description of the Prior Art
The rapid anionic polymerization of lactams in general, and, caprolactam in particular, to polyamide or polylactam polymers has long been known and practiced in the art. Further, it is known that the copolymerization of lactams in the presence of polyols provides very fast polymerizing systems suitable for the preparation of RIM (reaction injection molded) parts (see U.S. Pat. Nos. 3,862,262; 4,031,164 and 4,034,015).
In the patents cited supra the lactam monomer and polyol are polymerized in the presence of a lactam polymerization catalyst and either acyl polylactam or polyacyl lactam with the latter two reactants serving as the units which couple the recurring amide and polyol residues in the polymer chains. In an optional embodiment, the polyols and acyl polylactam or polyacyl lactams can be prereacted prior to the lactam polymerization.
We have now discovered what we believe to be a new class of polyamide block copolymers wherein residues of polymeric polyols or polymeric polyamines serve as the central soft segment block for the copolymer with the polyamide blocks attached to terminal positions of the soft segment. The polyamide blocks are attached to the soft segments through linkages which are entirely different from the residues arising from the acyl polylactams and polyacyl lactams of the prior art. The linkages in the present copolymers provide sites which can be substituted by a variety of groups thereby serving as a means for modifying the polymer properties.